When I try to download files through a sandbox web browser session by clicking on download links or by waiting for downloads to start automatically my browser freezes. Atm I just have IE11 but I can't try this on anything else as I can't download new installers due to this problem

I am running Windows 8.1 64-bit, Sandboxie was pretty much the first application installed (followed by AVAST) and there isn't much else installed on my computer that isn't in a sandbox. (Note this issue happens even in a new sandbox)
Any idea what might be causing this?